1. Field of the Invention
This invention relates generally to the fabrication of a thin film magnetic write head and more particularly to the use of a novel photoresist process that permits an improved fabrication process for such heads having ultra-short yokes.
2. Description of the Related Art
The size reduction of yoke length (YL) in thin film head (TFH) magnetic write heads to lengths less than 15 microns (μm) has necessitated the development of methods for obtaining flat insulator topographies. The short YL insulator resist imaging process currently used in the TFH fabrication industry results in a convex shape after thermal hardbake of the resist (FIG. 1). This shape is highly disadvantageous for the formation of a second magnetic coil layer and not only makes such second coil formation nearly impossible but also causes electrical shorting between the turns and between the turns and the magnetic pole yoke, leading to poor yields in terms of resistance and inductance values. Given that there will be a trend to higher insulator surface tensions as a result of the necessity of fabricating increasingly smaller yoke structures, the problems associated with dome-shaped insulators need to be resolved.
Chang et al. (U.S. Pat. No. 6,158,107) teach a method of fabricating a write head in which a second pole tip layer is plated over a write gap layer and a first tip layer within a soft-baked photoresist plating frame. The photoresist plating frame allows the gap layer and second tip layer to be self aligned with the first tip layer. The method of Chang et al., however, does not specifically teach how to form a photoresist layer that defines the insulated coil structures that are formed beneath the upper yoke. Neither does the method of Chang et al. disclose an ultra-short yoke. In fact, Chang et al. speak only of forming a second coil over a lapped surface. Krounbi et al. (U.S. Pat. No. 5,926,349) teach a method of forming a merged magnetoresistive (MR) head in which a double resistive layer is soft-baked over a single coil layer and then hard-baked for smoothness. The method neither teaches a second coil formation over the first, nor does it teach the formation of an ultra-short yoke. Chesnutt et al. (U.S. Pat. No. 6,105,238) teach a method for forming a write head structure in which any number of coil layers are allowed. They show, in particular, a two coil structure in which a first coil layer is covered by a first coil insulator (203 in their FIG. 2) that comprises, for example, a cured photoresist which can be an AZ4000 series positive photoresist. A second coil layer is then formed on this cured photoresist layer. Chesnutt et al. do not teach this method in the context of an ultra-short yoke, in fact they do not indicate the length of their yoke.
Terunuma et al (U.S. Pat. No. 6,151,193) teach a method of forming a magnetic write head in which a coil structure is formed on a flat, non-magnetic insulating film. They state that the coil film and its supporting insulating film can be formed on the flattened non-magnetic insulating film so as to eliminate disconnection and shorting of the coil film. Terunuma et al. do not disclose the length of the yoke structure, nor do they indicate the surface shape of the coil insulating film on which they would form a second coil layer.
Han et al. (U.S. Pat. No. 6,024,886) teach a method of forming a magnetic write head in which a flat surface is formed by means of a planarized, backfilling insulator layer. A single coil layer is formed on this planarized layer and then covered by a photoresist layer. Han et al. do not teach the formation of a second coil layer over the photoresist surface that covers the first coil layer, so it is not known what the surface shape of this layer is or what effect it would have on the formation of subsequent coil layers, if any. In addition, Han et al. do not disclose the yoke dimensions of their write head, so it is not known if it is an ultra-short write head,
Santini (U.S. Pat. No. 6,111,724) teaches a method of forming a magnetic write head with a novel pole tip structure by using a positive photoresist photopatterned over a negative resist layer. Although primarily teaching the tip formation, Santini also teaches the formation of a double coil layer and the insulation layer within which it is formed. The teaching does not indicate the method by which the second coil is formed over the surface of the insulation layer covering the first coil, nor does it indicate the length of the coil region.
As has already been pointed out, new problems with insulation layers and multiple coil layers arise in the context of ultra-short yoke lengths. In these cases, the surface tension of the photoresist layer that forms the insulation layer produces a convex surface on which it is extremely difficult to form a second coil layer. The prior art cited above does not address ultra-short yoke length fabrications and is, therefore, silent on the issue of photoresist surfaces and coil formation under those conditions. What is needed, therefore, is a method of forming a resistive layer for an ultra-short yoke fabrication wherein the surface of the layer is flat in the region of coil formation and yet the layer achieves a desired apex angle.